The present invention is directed towards a head rotation apparatus for a video tape recorder, i.e. the component assembly within a video recorder which mounts and rotates the record/reproduce heads with respect to the video tape. Such an apparatus is disposed within a cylindrical fixed drum (generally referred to as the guide drum) having a peripheral slit formed therein, within which the tips of the heads rotate against the video tape, which is guided to move diagonally around the guide drum. In this way, successive diagonally oriented tracks are recorded on the video tape as the heads rotate and the tape moves over the guide drum, with the rotation of the heads serving to increase the relative speed between the heads and the video tape, to maximize the recording frequency response. In particular, the invention is directed towards a head rotation apparatus which is provided with both fixed heads and movable heads, i.e. heads which can be controllably displaced along the axis of rotation of the heads by means of drive voltages. Such movable heads are necessary to produce certain special effects with a video tape recorder, such as slow-motion or stationary reproduction of recorded material. When such special modes of reproduction are carried out, the relative velocity between the heads and the video tape will in general be different from that at the time of recording, and as a result the direction of the path traced out of each head over the video tape will differ from that of the recorded tracks, i.e. will form a certain angle with respect to the recorded tracks. For this reason, it is necessary to compensate the head movement such that the heads being used for reproduction will accurately follow the previously recorded tracks on the video tape. This can be accomplished by moving the heads in the direction of the axis of rotation of the heads, at a suitable rate, such as to move along the paths of the originally recorded tracks while reporduction is in progress. A method of executing such movement of the heads which is well-known in the art is to mount one or more heads on members having electrodes disposed thereon, the members being formed of a material which exhibits deflection in response to voltages applied to the electrodes, with the magnitude of the deflection being determined by the amplitude of the applied voltage. Suitable materials for this purpose include bimorph ceramics. Such movable heads, and means for controlling the head movement, are disclosed in Japanese patent laid-open 52-117106 and publication 56-50329.
It is an essential condition for a recording head assembly incorporating such movable heads, generally mounted in conjunction with fixed heads, that the "home position" of each movable head (i.e. the position of the head in the absence of voltage applied to the corresponding deflection member) is accurately defined with respect to the fixed heads and the axis of rotation. In general, two diametrically opposed fixed heads are utilized, mounted on a head drum which is driven by a motor, with two movable heads being mounted diametrically opposed on a ring-shaped deflection member. This deflection member is held clamped with respect to the head drum at positions 90.degree. apart from the movable heads, i.e. the movable heads are disposed 90.degree. apart from the fixed heads. Electrodes are formed on the respective halves of the deflection member, divided in this manner, so that the two movable heads can be independently moved along the direction of the axis of rotation by control voltages applied to the respective halves of the deflection member. In the prior art, however, the mechanical configuration adopted for the means whereby the movable heads (i.e. in the "home position") are aligned accurately with respect to the fixed heads and the axis of rotation are relatively complex, and require that a plurality of surfaces which are disposed in different planes be machined to an extremely high degree of precision. Thus, such an assembly is expensive to manufacture, and is difficult to make light in weight and compact, as will be made clear from a description of an example of such a prior art type of head rotation appratus.
It is therefore an objective of the present invention to provide an improved head rotation apparatus, whereby the disadvantages of the prior art described above may be overcome, by ensuring that the requisite degree of accuracy of positioning the movable heads can be attained with a simpler and more easily manufactured configuration.